The present invention relates to osmium oxide microencapsulated in an aromatic polyolefin and osmium oxidechial ligand complex microencapsulated in an aromatic polyolefin, which makes it possible to conduct an oxidation reaction of organic compounds in an enlarged industrial production scale.
It has been said that, among osmium oxide compounds, only oxides of tetravalent and octavalent osmium are actually existing in separated form, but additionally, oxides of divalent, trivalent and hexavalent osmium may be considered to exist. The oxides of octavalent osmium have been called osmium tetroxide or osmic acid when it is in an aqueous solution, and the oxides show a strong oxidation ability and thus they have been used as a special oxidizing agent and a catalyst in an organic synthesis. However, osmium tetroxide shows a melting point of 40.6 to 40.7.degree. C., a boiling point of 131.2.degree. C. and vapor pressure of 7 mm at 20.degree. C. (or 52 mm at 55.degree. C.), and has peculiar smell which can be perceived even in such an extraordinary low concentration as 2.times.10.sup.-5 mg/ml, and further its vapor affects a mucosa of eye, among others, and is toxic to all respiratory organs.
Therefore, use of osmium tetroxide in an industrial scale has been troublesome, and it has been used only as an oxidizing agent for oxidizing a small amount of precious substances. Actually some technologies have been tried for the purpose of using this compound safely in an industrial scale. For instance, International Patent Publication (in Japanese) No. 505884/1992 provides a method for precipitating an osmium oxide on nitrogen-containing polymer from a solvent solution, and actually a product comprising about 1 wt % of osmium tetroxide immobilized on poly(4-vinylpyridine) (e.g. listed on a catalogue of Sigma-Aldrich) has been on the market.
However, in all of those known methods, all basic polymers containing nitrogen atoms, particularly cross-linked ones, have been used to utilize chemical binding effect between the osmium oxide and quaternary nitrogen atoms, and therefore their production has not been easy. Further, when those known compositions are used in actual reactions, the polymers immobilizing the osmilm oxide are gradually decomposed under oxng conditions (Journal of Molecular Catalysis A: Chemical, vol. 120 (1997) p 203 right column), and therefore the problems upon handling have not yet been solved, and reuse of the compositions is still restricted.
Further, in the product disclosed in the above International Patent Publication (in Japanese) No. 505884/1992, as stated therein, the osmium oxide immobilized on polymer containing nitrogen atoms does not exist in the form of osmium tetroxide but in the form of osmium trioxide or, sometimes, oxide of a polymer or in a reduced form such as oxoanion, and thus it cannot be said that the osmnium oxide is immobilized on the polymer as the stable form of osmium tetroxide and consequently the effect as an oxidizing agent of the product is apparently poor as compared with that of osmium tetroxide.
Recently, it is reported that oxidation of olefin compounds by using osmium oxide to which a chiral ligand is attached can give the corresponding chiral products ("Catalytic asymmetric synthesis, VHC Publisher, New York, 1993, P.227-272," or "Chem. Rev., 94, 2483-2547 (1994)," etc.). But in those asymmetric oxidations, an osmium oxide itself is used without, for instance, nnmobilized on polymers, etc., and therefore, the recovery and reuse of the osmium oxide is usually difficult.
On the other hand, it is reported that an asymmetric oxidation is conducted using a complex of an osmium tetroxide and a polymer on which a chiral ligand is immobilized ("Eur. J. Org. Chem., 1998, 21-27" etc). However, in this method, introducing of the chiral ligand in the polymer is not so easy and further the polymer containing the chiral ligand thus obtained has to be farther reacted with osmium tetroxide. Additionally, the osmium tetroxide in the complex comes off from the complex little by little during the asymmetric oxidation, and therefore reuse of the complex many times is substantially impossible.